The present invention relates generally to non-thermal plasma reactors for use in conjunction with internal combustion engines and, more particularly, to a method for providing uniform barrier discharge in a parallel plate, monolithic plasma reactor.
Non-thermal plasma has shown promise as a means for reducing nitrogen oxide (NOx) emissions found in the exhaust gas of an internal combustion engine of a motor vehicle. Although there are several well known non-thermal reactor designs, many of these designs are not able to withstand the wide temperature swings and vibrations associated with a motor vehicle. To properly function in the context of a motor vehicle, a parallel plate, monolithic reactor was developed by the assignee of the present invention.
However, the parallel plate, monolithic plasma reactor exhibits non-uniform plasma distribution during certain engine operating conditions. Although exhaust gas is successfully treated during low flow conditions, the monolithic plasma reactor may exhibit non-uniform plasma distribution during high flow conditions. In order to properly treat the exhaust gas, the plasma reactor must supply more power (i.e., energy density) into the exhaust gas at the elevated flow conditions. There are generally two ways to increase the energy density going into the exhaust gas. A first way is to increase the peak voltage of the applied electrical signal. However, increasing the voltage amplitude is limited by the dielectric strength of the ceramic sheets that form the parallel plate, monolithic plasma reactor. A second way is to increase the frequency of the alternating current electrical signal. In this case, increasing the frequency of the electrical signal substantially increases the non-uniformity of the plasma distribution in the monolithic plasma reactor. This in turn results in non-uniform gas treatment.
Thus, there is a need for providing uniform plasma distribution over a wide range of engine operating conditions handled by a non-thermal plasma reactor in a motor vehicle.
In accordance with the present invention, an exhaust treatment system is provided for use with an internal combustion engine in a motor vehicle. The exhaust treatment system includes a parallel plate, monolithic plasma reactor for reducing nitrogen oxides in the exhaust gas from the engine, an electric power source for providing an electrical signal to the electrodes of the plasma reactor, and a controller interconnected between the electric power source and the plasma reactor for modulating the electrical signal to the plasma reactor. More specifically, the electric power source provides an alternating current electrical signal and the controller modulates the electrical signal off in accordance with a predetermined duty cycle, thereby achieving uniform barrier discharge in the plasma reactor.
For a more complete understanding of the invention, its objects and advantages, refer to the following specification and to the accompanying drawings.